mm: consolidate the get_user_pages* implementations

Always build mm/gup.c so that we don't have to provide separate nommu
stubs.  Also merge the get_user_pages_fast and __get_user_pages_fast stubs
when HAVE_FAST_GUP into the main implementations, which will never call
the fast path if HAVE_FAST_GUP is not set.

This also ensures the new put_user_pages* helpers are available for nommu,
as those are currently missing, which would create a problem as soon as we
actually grew users for it.

Link: http://lkml.kernel.org/r/20190625143715.1689-13-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: James Hogan <jhogan@kernel.org>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -133,6 +133,7 @@ config HAVE_MEMBLOCK_PHYS_MAP
 	bool
 
 config HAVE_FAST_GUP
+	depends on MMU
 	bool
 
 config ARCH_KEEP_MEMBLOCK

mm/Makefile

@@ -22,7 +22,7 @@ KCOV_INSTRUMENT_mmzone.o := n
 KCOV_INSTRUMENT_vmstat.o := n
 
 mmu-y			:= nommu.o
-mmu-$(CONFIG_MMU)	:= gup.o highmem.o memory.o mincore.o \
+mmu-$(CONFIG_MMU)	:= highmem.o memory.o mincore.o \
 			   mlock.o mmap.o mmu_gather.o mprotect.o mremap.o \
 			   msync.o page_vma_mapped.o pagewalk.o \
 			   pgtable-generic.o rmap.o vmalloc.o
@@ -39,7 +39,7 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   mm_init.o mmu_context.o percpu.o slab_common.o \
 			   compaction.o vmacache.o \
 			   interval_tree.o list_lru.o workingset.o \
-			   debug.o $(mmu-y)
+			   debug.o gup.o $(mmu-y)
 
 # Give 'page_alloc' its own module-parameter namespace
 page-alloc-y := page_alloc.o

mm/gup.c

@@ -134,6 +134,7 @@ void put_user_pages(struct page **pages, unsigned long npages)
 }
 EXPORT_SYMBOL(put_user_pages);
 
+#ifdef CONFIG_MMU
 static struct page *no_page_table(struct vm_area_struct *vma,
 		unsigned int flags)
 {
@@ -1322,6 +1323,51 @@ struct page *get_dump_page(unsigned long addr)
 	return page;
 }
 #endif /* CONFIG_ELF_CORE */
+#else /* CONFIG_MMU */
+static long __get_user_pages_locked(struct task_struct *tsk,
+		struct mm_struct *mm, unsigned long start,
+		unsigned long nr_pages, struct page **pages,
+		struct vm_area_struct **vmas, int *locked,
+		unsigned int foll_flags)
+{
+	struct vm_area_struct *vma;
+	unsigned long vm_flags;
+	int i;
+
+	/* calculate required read or write permissions.
+	 * If FOLL_FORCE is set, we only require the "MAY" flags.
+	 */
+	vm_flags  = (foll_flags & FOLL_WRITE) ?
+			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
+	vm_flags &= (foll_flags & FOLL_FORCE) ?
+			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
+
+	for (i = 0; i < nr_pages; i++) {
+		vma = find_vma(mm, start);
+		if (!vma)
+			goto finish_or_fault;
+
+		/* protect what we can, including chardevs */
+		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
+		    !(vm_flags & vma->vm_flags))
+			goto finish_or_fault;
+
+		if (pages) {
+			pages[i] = virt_to_page(start);
+			if (pages[i])
+				get_page(pages[i]);
+		}
+		if (vmas)
+			vmas[i] = vma;
+		start = (start + PAGE_SIZE) & PAGE_MASK;
+	}
+
+	return i;
+
+finish_or_fault:
+	return i ? : -EFAULT;
+}
+#endif /* !CONFIG_MMU */
 
 #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
 static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
@@ -1484,7 +1530,7 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
 {
 	return nr_pages;
 }
-#endif
+#endif /* CONFIG_CMA */
 
 /*
  * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
@@ -2160,6 +2206,12 @@ static void gup_pgd_range(unsigned long addr, unsigned long end,
 			return;
 	} while (pgdp++, addr = next, addr != end);
 }
+#else
+static inline void gup_pgd_range(unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages, int *nr)
+{
+}
+#endif /* CONFIG_HAVE_FAST_GUP */
 
 #ifndef gup_fast_permitted
 /*
@@ -2177,6 +2229,9 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
  * the regular GUP.
  * Note a difference with get_user_pages_fast: this always returns the
  * number of pages pinned, 0 if no pages were pinned.
+ *
+ * If the architecture does not support this function, simply return with no
+ * pages pinned.
  */
 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			  struct page **pages)
@@ -2206,7 +2261,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	 * block IPIs that come from THPs splitting.
 	 */
 
-	if (gup_fast_permitted(start, end)) {
+	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
+	    gup_fast_permitted(start, end)) {
 		local_irq_save(flags);
 		gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr);
 		local_irq_restore(flags);
@@ -2214,6 +2270,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 
 	return nr;
 }
+EXPORT_SYMBOL_GPL(__get_user_pages_fast);
 
 static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
 				   unsigned int gup_flags, struct page **pages)
@@ -2270,7 +2327,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 	if (unlikely(!access_ok((void __user *)start, len)))
 		return -EFAULT;
 
-	if (gup_fast_permitted(start, end)) {
+	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
+	    gup_fast_permitted(start, end)) {
 		local_irq_disable();
 		gup_pgd_range(addr, end, gup_flags, pages, &nr);
 		local_irq_enable();
@@ -2296,5 +2354,4 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 
 	return ret;
 }
-
+EXPORT_SYMBOL_GPL(get_user_pages_fast);
-#endif /* CONFIG_HAVE_GENERIC_GUP */

mm/nommu.c

@@ -111,94 +111,6 @@ unsigned int kobjsize(const void *objp)
 	return PAGE_SIZE << compound_order(page);
 }
 
-static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
-		      unsigned long start, unsigned long nr_pages,
-		      unsigned int foll_flags, struct page **pages,
-		      struct vm_area_struct **vmas, int *nonblocking)
-{
-	struct vm_area_struct *vma;
-	unsigned long vm_flags;
-	int i;
-
-	/* calculate required read or write permissions.
-	 * If FOLL_FORCE is set, we only require the "MAY" flags.
-	 */
-	vm_flags  = (foll_flags & FOLL_WRITE) ?
-			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
-	vm_flags &= (foll_flags & FOLL_FORCE) ?
-			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
-
-	for (i = 0; i < nr_pages; i++) {
-		vma = find_vma(mm, start);
-		if (!vma)
-			goto finish_or_fault;
-
-		/* protect what we can, including chardevs */
-		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
-		    !(vm_flags & vma->vm_flags))
-			goto finish_or_fault;
-
-		if (pages) {
-			pages[i] = virt_to_page(start);
-			if (pages[i])
-				get_page(pages[i]);
-		}
-		if (vmas)
-			vmas[i] = vma;
-		start = (start + PAGE_SIZE) & PAGE_MASK;
-	}
-
-	return i;
-
-finish_or_fault:
-	return i ? : -EFAULT;
-}
-
-/*
- * get a list of pages in an address range belonging to the specified process
- * and indicate the VMA that covers each page
- * - this is potentially dodgy as we may end incrementing the page count of a
- *   slab page or a secondary page from a compound page
- * - don't permit access to VMAs that don't support it, such as I/O mappings
- */
-long get_user_pages(unsigned long start, unsigned long nr_pages,
-		    unsigned int gup_flags, struct page **pages,
-		    struct vm_area_struct **vmas)
-{
-	return __get_user_pages(current, current->mm, start, nr_pages,
-				gup_flags, pages, vmas, NULL);
-}
-EXPORT_SYMBOL(get_user_pages);
-
-long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
-			    unsigned int gup_flags, struct page **pages,
-			    int *locked)
-{
-	return get_user_pages(start, nr_pages, gup_flags, pages, NULL);
-}
-EXPORT_SYMBOL(get_user_pages_locked);
-
-static long __get_user_pages_unlocked(struct task_struct *tsk,
-			struct mm_struct *mm, unsigned long start,
-			unsigned long nr_pages, struct page **pages,
-			unsigned int gup_flags)
-{
-	long ret;
-	down_read(&mm->mmap_sem);
-	ret = __get_user_pages(tsk, mm, start, nr_pages, gup_flags, pages,
-				NULL, NULL);
-	up_read(&mm->mmap_sem);
-	return ret;
-}
-
-long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
-			     struct page **pages, unsigned int gup_flags)
-{
-	return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
-					 pages, gup_flags);
-}
-EXPORT_SYMBOL(get_user_pages_unlocked);
-
 /**
  * follow_pfn - look up PFN at a user virtual address
  * @vma: memory mapping

mm/util.c

@@ -300,53 +300,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 }
 #endif
 
-/*
- * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
- * back to the regular GUP.
- * Note a difference with get_user_pages_fast: this always returns the
- * number of pages pinned, 0 if no pages were pinned.
- * If the architecture does not support this function, simply return with no
- * pages pinned.
- */
-int __weak __get_user_pages_fast(unsigned long start,
-				 int nr_pages, int write, struct page **pages)
-{
-	return 0;
-}
-EXPORT_SYMBOL_GPL(__get_user_pages_fast);
-
-/**
- * get_user_pages_fast() - pin user pages in memory
- * @start:	starting user address
- * @nr_pages:	number of pages from start to pin
- * @gup_flags:	flags modifying pin behaviour
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_pages long.
- *
- * get_user_pages_fast provides equivalent functionality to get_user_pages,
- * operating on current and current->mm, with force=0 and vma=NULL. However
- * unlike get_user_pages, it must be called without mmap_sem held.
- *
- * get_user_pages_fast may take mmap_sem and page table locks, so no
- * assumptions can be made about lack of locking. get_user_pages_fast is to be
- * implemented in a way that is advantageous (vs get_user_pages()) when the
- * user memory area is already faulted in and present in ptes. However if the
- * pages have to be faulted in, it may turn out to be slightly slower so
- * callers need to carefully consider what to use. On many architectures,
- * get_user_pages_fast simply falls back to get_user_pages.
- *
- * Return: number of pages pinned. This may be fewer than the number
- * requested. If nr_pages is 0 or negative, returns 0. If no pages
- * were pinned, returns -errno.
- */
-int __weak get_user_pages_fast(unsigned long start,
-				int nr_pages, unsigned int gup_flags,
-				struct page **pages)
-{
-	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
-}
-EXPORT_SYMBOL_GPL(get_user_pages_fast);
-
 unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
 	unsigned long len, unsigned long prot,
 	unsigned long flag, unsigned long pgoff)